Sudden cardiac death (SCD), or cardiac arrest, is the sudden, abrupt loss of heart function in a person who may or may not have diagnosed heart disease. Sudden cardiac death may be caused by almost all known heart diseases. Most cardiac arrests occur when the diseased heart begins to exhibit rapid and/or chaotic activity—ventricular tachycardia or fibrillation. Some are due to extreme slowing of the heart. All these events are called life-threatening arrhythmias. Patient's implanted with an implantable medical device, such as an implantable cardioverter defibrillator (ICD), greatly increase their chances of preventing sudden cardiac death caused by sustained ventricular arrhythmias. However, there are a significant number of patients with an increased propensity for suffering sudden cardiac death who have not experienced and survived previous cardiac episodes and therefore who are not already implanted with an implantable medical device. Consequently, there is a need for techniques and apparatus that can identify individuals at risk for sudden cardiac death prior to the onset of identifiable symptoms in order to provide those patients with an appropriate preventative therapy, such as drug therapy and/or an IMD that provides electrical stimulation therapy.